The major objective of the proposed research is to better understand the regulation of ornithine decarboxylase (ODC) activity in Swiss 3T3 cells during the transition from a relatively slowly growing to a more rapidly proliferating state. During the first several hours of this transition, ODC activity increases 50-100 fold, falls to about 60% of this level, and then increases once again. We will investigate during this period the amount of ODC, the rates of synthesis and degradation of ODC, and the existence of, and possible interconversion of multiple forms of ODC which differ in their activity. Also, because there is much indirect evidence that polyamines may limit their own synthesis by specifically inhibiting the translation of ODC message, we will explore this possibility directly by quantitating ODC synthesis in intact cells as well as in cell-free protein-synthesizing systems in the presence and absence of added polyamines. We will measure the total amount of ODC by immunotitration in conjunction with residual activity measurements. We will measure the synthesis of ODC by a brief radioactive labeling, and the degradation of ODC by determining residual radioactivity at intervals after a relatively extended pulse-labeling. The synthesis and degradation studies will require quantitative immunoprecipitation by natural or derived monospecific antibody and controls for nonspecific precipitation and/or dissociation of the antigen/antibody complex followed by gel electrophoresis to ensure a neglible background of radioactive proteins. We will improve our isolation procedures for the two forms of ODC which differ in their PLP affinity and then use these procedures to measure the relative contribution of the two forms to total ODC activity as the stimulation period progresses. We will also intensify our efforts to find other evidence of forms of ODC which may differ in their activity.